I want to be in the loop area of Chicago and not sure if the blue line from the airport is still having works done. Few delays and packed trains last time I went back to the airport, and the time before that, replacement buses in places.

Anyway, I changed to an evening train the day before. Supposed to get in at 10:44pm, and then up to 15 mins or so walk to my hotel, but not too fussed if it were running late.
(Would rather stay the night in Chicago to be honest than St Louis, and get up around 6am for an 8am departure.)

Flights are £200+ now, so even more of a bargain on the train.
(Did look at redemptions using BA Avios, but nothing on the day I want to travel after 10am which is too early. Next day, either early; too much for a 1h20 flight; later in the day that reduces my Chicago time)

I'll give it a shot. Either it will be an experience and a half, or work out fairly well for me.

Have taken Amtrak between PHL and NYC before and that was fine. Bit of a rush to get a seat, but got a window and the train filled up. Comfy and not that bad an experience for the $20-$25 it cost me..